The present invention relates to the field of extraction of high molecular weight DNA from test samples, particularly from human whole blood samples.
The present invention is an improvement on the apparatus and process previously described and claimed in a related application, Ser. No. 714,376, now U.S. Pat. No. 4,617,102, assigned to the assignee of the present application. In that related application, the basic process and apparatus are directed to the collection of DNA of usable volume and concentration and of such purity as to permit conventional restriction by a number of enzymes without the need for further purification. Essentially, the apparatus described in the related application consists of an agarose gel disk, typically 5 millimeters thick by 31 millimeters in diameter, which is immersed in an electrophoresis buffer solution and supported between 8 micrometer polycarbonate filters in an electric field.
Considered in some detail, the process of the related U.S. Pat. No. 4,617,102 involves the loading of a suitably treated sample, such as blood lysate, onto the top face of the agarose gel disk and then applying the electric field. It turns out that of the total constituent parts of the treated blood, the DNA molecules are by far the largest in respect to molecular weight. Consequently, their passage through the agarose gel disk, under the force of the electric field, is impeded such that the time period governing their removal is substantial. All other constituent parts of the treated blood pass relatively rapidly through the gel disk and are readily removed, being swept away by flow of the buffer solution. The DNA is then eluted and collected in concentrated form by application of the electric field, while the normal flow of buffer solution between the bottom of the gel matrix and a collection chamber is prevented. Other and further details of the constuction of the DNA extraction apparatus may be appreciated from the cited related application, such details being incorporated herein by reference where appropriate.
Although the process and apparatus described in the related application, and briefly summarized above, have functioned to provide DNA of usable volume and concentration, it turns out to be highly desirable to be able to operate even more efficiently in the processing of a blood lysate sample for removal of DNA, particularly to be able simply and quickly to remove a given collection cup, in which the DNA has been recovered, from the machine or apparatus, and to replace it immediately with an identical collection cup. The DNA captured on the membrane in the given collection cup is then removed for further processing. The gel matrix retainer member associated with the collection cup is normally the only disposable unit; however, the entire assembly could be made disposable. As a consequence of this replaceable construction, the processing operation can be made substantially continuous.
Accordingly, it is a primary object of the present invention to further reduce the processing times involved in the operation of extracting the DNA from test samples.
Another object is to provide a more efficient way of removing all of the unwanted constituents from the blood lysate or other sample when that part of the procedure is being carried out and, likewise, to readily remove from the machine or apparatus the collection cup in which the DNA has been collected; furthermore, to be able easily and quickly to separate the individual parts of the collection cup when so removed, thereby to have access to the collected DNA.
Another object is to provide a simpler mechanism--and one that permits more relaxed tolerances on parts--for collecting the laminar flow of buffer solution at the different stages in the operation of the DNA extraction process.